Honda Car Forum

I heard that they increase the amount of exhaust output, which in turn increases horsepower..

they are great if balanced with a modified intake/intake manifold and can offer up to an additional 20hp in some 4 cylinders. but, they are illegal in most states and tree huggers hate them because by bypassing the catylic converter you are going to be allowing higher Co2 emissions.

When optimizing an engine for the greatest LEGAL horsepower in street applications, one of the most limiting factors in the exhaust system is the catalytic converter. It is required in all fifty states for emission controls and is illegal to remove or bypass.If you improve the air flow capability of your engine, it will breathe easier and produce more horsepower. To do that, you would have to reduce the constriction in the exhaust produced by the stock catalytic converter yet still be legal. That's where the hi-flow cat comes in. Some aftermarket parts are not legal in all fifty states and California is one of the worst but then has some of the worst air pollution too.You must understand that adding this cat may increase your NOx output beyond legal limits and be required to be removed but I seriously doubt it and would talk directly with the manufacturer of the hi-flow cat to be sure before spending big dollars on one.Just remember... increasing the capability of the exhaust without increasing the capability of the intake system does you little good. Doing both and then reprogramming the computer (mod chip) would squeeze 50-60 more horses out of your stock engine. It doesn't come without additional expenses though... you will be paying for that extra performance at the pump.Good luck!

Pro more power and flow. The only Con is some times the rear heated exhaust O2 sensor might not respond correctly.